User:Falkirks/sandbox/UDID

A UDID is a 40-character alphanumeric string assigned to certain device marketed by Apple. These devices include iPhone, iPad and iPod (touch).

Structure
A UDID is a strong composed of lowercase letters and numbers. These strings are always 40 characters. Letters in the UDID string are never further in the alphabet than the letter e. Below is a sample UDID: 51a768800415fd8f08dc14a85453ab6cc8a96f5b

Retrival
While UDID's area not available directly on a non-jailbroken IOS a number of third part apps in apple's AppStore allow users to get their UDID. Apple's SDK does allow developers to retrieve the device UDID but as of March 2013 they won't accept any new apps or updates to the AppStore that use this feature. A device UDID can also be retrieved using apple's iTunes or a similar desktop application.